diff --git a/src/jwkest/jws.py b/src/jwkest/jws.py
index a8c957d..1b2464e 100644
--- a/src/jwkest/jws.py
+++ b/src/jwkest/jws.py
@@ -406,6 +406,22 @@ def _pick_keys(self, keys, use="", alg=""):
 
         return pkey
 
+    def _pick_alg(self, keys):
+        alg = None
+        try:
+            alg = self["alg"]
+        except KeyError:
+            # try to get alg from key if there is only one
+            if keys is not None and len(keys) == 1:
+                key = next(iter(keys))  # first element from either list or dict
+                if key.alg:
+                    self["alg"] = alg = key.alg
+
+        if not alg:
+            self["alg"] = alg = "none"
+
+        return alg
+
     def _decode(self, payload):
         _msg = b64d(bytes(payload))
         if "cty" in self:
@@ -420,13 +436,7 @@ def dump_header(self):
 class JWS(JWx):
 
     def alg_keys(self, keys, use, protected=None):
-        try:
-            _alg = self["alg"]
-        except KeyError:
-            self["alg"] = _alg = "none"
-        else:
-            if not _alg:
-                self["alg"] = _alg = "none"
+        _alg = self._pick_alg(keys)
 
         if keys:
             keys = self._pick_keys(keys, use=use, alg=_alg)
diff --git a/src/jwkest/jwt.py b/src/jwkest/jwt.py
index 7a54ac0..5dc80c8 100644
--- a/src/jwkest/jwt.py
+++ b/src/jwkest/jwt.py
@@ -17,13 +17,15 @@ def split_token(token):
 def b2s_conv(item):
     if isinstance(item, bytes):
         return item.decode("utf-8")
-    elif isinstance(item, (six.string_types, int, bool)):
+    elif item is None or isinstance(item, (six.string_types, int, bool)):
         return item
     elif isinstance(item, list):
         return [b2s_conv(i) for i in item]
     elif isinstance(item, dict):
         return dict([(k, b2s_conv(v)) for k, v in item.items()])
 
+    raise ValueError("Can't convert {}.".format(repr(item)))
+
 
 def b64encode_item(item):
     if isinstance(item, bytes):
diff --git a/tests/test_1_jwt.py b/tests/test_1_jwt.py
index 0c8785d..72e1057 100644
--- a/tests/test_1_jwt.py
+++ b/tests/test_1_jwt.py
@@ -1,5 +1,8 @@
 import json
-from jwkest.jwt import JWT
+
+import pytest
+
+from jwkest.jwt import JWT, b2s_conv
 
 __author__ = 'roland'
 
@@ -44,6 +47,10 @@ def test_unpack_str():
     assert _jwt2
     out_payload = _jwt2.payload()
 
+def test_b2s_conv_raise_exception_on_bad_value():
+    with pytest.raises(ValueError):
+        b2s_conv(object())
+
 
 if __name__ == "__main__":
     test_unpack_str()
diff --git a/tests/test_3_jws.py b/tests/test_3_jws.py
index 11fbe09..316a43e 100644
--- a/tests/test_3_jws.py
+++ b/tests/test_3_jws.py
@@ -505,6 +505,19 @@ def test_rs256_rm_signature():
     else:
         assert False
 
+def test_pick_alg_assume_alg_from_single_key():
+    expected_alg = "HS256"
+    keys = [SYMKey(k="foobar", alg=expected_alg)]
+
+    alg = JWS()._pick_alg(keys)
+    assert alg == expected_alg
+
+def test_pick_alg_dont_get_alg_from_single_key_if_already_specified():
+    expected_alg = "RS512"
+    keys = [RSAKey(key=import_rsa_key_from_file(KEY), alg="RS256")]
+
+    alg = JWS(alg=expected_alg)._pick_alg(keys)
+    assert alg == expected_alg
 
 if __name__ == "__main__":
     test_rs256_rm_signature()